1. Technical Field
The present invention relates generally to an improved data processing system and in particular to a method and apparatus for accessing data on a storage device. Still more particularly, the present invention relates to a method and apparatus for accessing data on storage media in the form of a tape.
2. Description of Related Art
Tape drives are peripheral mass storage devices often used to archive data on tapes for later access. Tape drives are also used as random access devices in data storage applications where cost of storage might be important and access time is of less significance. For example, many banks and financial institutions, insurance companies, and government agencies may use tape drives with applications regarding clients, accounts, patients, and other items of interest. In other applications, huge amounts of data are stored directly on tape for later retrieval and analysis.
In accessing data on a tape, a read or write head in a tape drive is positioned over one or more tracks on the tape. A servo track may be used for aligning the read or write head to the tracks containing the data. If the read or write head drifts from an optimal position relative to the track on the tape, an error signal is generated. The error signal increases as the read or write head drifts further from the optimal location relative to the data on the track on the tape. If the read or write head drifts too far relative to the data on the track, errors and data recovery problems occur in accessing the tape. Presently available systems adjust the position of the read or write head or the position of the tape relative to the read or write head to minimize the error signal generated during access of the tape.
Evidence indicates that, over time, tape dimensions are distorted over the length of the tape. In addition, tape distortion can worsen with a combination of time, temperature, and use. Three primary problems result from tape distortion. First, the data tracks on the tape can shift position relative to the data readers, resulting in the loss or overwriting of data. Second, distorted servo tracks can degrade the ability of the tape servo system to acquire and follow the servo tracks, resulting in degraded performance. Third, tape distortion requires the costly development of robustness in the tape drive, which would allow the servo system to handle tapes that exceed distortion specifications.
In addition, as data tracks become narrower in the future, the margins of error in tape distortion will decrease even further.
Therefore, it would be desirable to have a method for detecting tape distortions that exceed established specifications.
The present invention provides a method, system and program for measuring magnetic tape track distortion. The invention comprises defining specifications for tape track distortion acceptability and using tape head servo readers to collect component position error signal (PES) data from servo tracks on a magnetic tape. The separate PES data are analyzed to determine tape distortion. The data can also be adjusted for reliability factors that might affect the confidence of the PES data. The distortion data for the tape is then compared to the defined specifications and a determination is made as to whether the tape meets acceptability standards.